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            <div><h3 class="title">
                <a name="asio.reference.Service"></a><a class="link" href="Service.html" title="Service requirements">Service
                requirements</a>
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    <p>
        A class is a <span class="emphasis"><em>service</em></span> if it is publicly and unambiguously
        derived from <code class="computeroutput"><span class="identifier">execution_context</span><span
            class="special">::</span><span class="identifier">service</span></code>,
        or if it is publicly and unambiguously derived from another service. For
        a service <code class="computeroutput"><span class="identifier">S</span></code>, <code
            class="computeroutput"><span class="identifier">S</span><span class="special">::</span><span
            class="identifier">key_type</span></code>
        shall be valid and denote a type (C++Std [temp.deduct]), <code class="computeroutput"><span class="identifier">is_base_of_v</span><span
            class="special">&lt;</span><span class="keyword">typename</span> <span class="identifier">S</span><span
            class="special">::</span><span class="identifier">key_type</span><span class="special">,</span> <span
            class="identifier">S</span><span class="special">&gt;</span></code>
        shall be <code class="computeroutput"><span class="keyword">true</span></code>, and <code
            class="computeroutput"><span class="identifier">S</span></code> shall satisfy the <code
            class="computeroutput"><span class="identifier">Destructible</span></code>
        requirements (C++Std [destructible]).
    </p>
    <p>
        The first parameter of all service constructors shall be an lvalue reference
        to <code class="computeroutput"><span class="identifier">execution_context</span></code>. This
        parameter denotes the <code class="computeroutput"><span class="identifier">execution_context</span></code>
        object that represents a set of services, of which the service object will
        be a member. [<span class="emphasis"><em>Note:</em></span> These constructors may be called
        by the <code class="computeroutput"><span class="identifier">make_service</span></code> function.
        —<span class="emphasis"><em>end note</em></span>]
    </p>
    <p>
        A service shall provide an explicit constructor with a single parameter of
        lvalue reference to <code class="computeroutput"><span class="identifier">execution_context</span></code>.
        [<span class="emphasis"><em>Note:</em></span> This constructor may be called by the <code
            class="computeroutput"><span class="identifier">use_service</span></code> function. —<span class="emphasis"><em>end note</em></span>]
    </p>
    <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">my_service</span> <span
            class="special">:</span> <span class="keyword">public</span> <span
            class="identifier">execution_context</span><span class="special">::</span><span
            class="identifier">service</span>
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
  <span class="keyword">typedef</span> <span class="identifier">my_service</span> <span
                class="identifier">key_type</span><span class="special">;</span>
  <span class="keyword">explicit</span> <span class="identifier">my_service</span><span class="special">(</span><span
                class="identifier">execution_context</span><span class="special">&amp;</span> <span class="identifier">ctx</span><span
                class="special">);</span>
  <span class="identifier">my_service</span><span class="special">(</span><span
                class="identifier">execution_context</span><span class="special">&amp;</span> <span class="identifier">ctx</span><span
                class="special">,</span> <span class="keyword">int</span> <span
                class="identifier">some_value</span><span class="special">);</span>
<span class="keyword">private</span><span class="special">:</span>
  <span class="keyword">virtual</span> <span class="keyword">void</span> <span class="identifier">shutdown</span><span
                class="special">()</span> <span class="keyword">noexcept</span> <span class="identifier">override</span><span
                class="special">;</span>
  <span class="special">...</span>
<span class="special">};</span>
</pre>
    <p>
        A service's <code class="computeroutput"><span class="identifier">shutdown</span></code> member
        function shall destroy all copies of user-defined function objects that are
        held by the service.
    </p>
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            <div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
                Distributed under the Boost Software License, Version 1.0. (See accompanying
                file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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